| |  | Continuing the discussion started on Wednesday, we examine some of probable steps in the origin of life on earth. | 
 |  | Life probably originated around 3.8 billion years ago. | 
 |  | The conditions on the earth were suitable for building life. | 
 |  | The building blocks of life were generated either by aboitic synthesis or arrived from extraterrestrial sources. | 
 |  | These building blocks were used to generate the protiens, nucleic acids, and organic phosphates necessary for life. | 
 |  | Life, once established, would change the environment so that life could not arise again. | 
 |  | Setting the stage, 3.8 Billion years ago | 
 |  | The earths atmosphere is rich in CO2, H2O, N2, lesser amounts of methane and amonia | 
 |  | Temperature at the earths surface drops below 100 C | 
 |  | Acidic rains fall, Erosion begins | 
 |  | UltraViolet light beats down | 
 |  | The earth's crust is thin and hot | 
 |  | Warm mineral-rich oceans form | 
 |  | The Building blocks of life | 
 |  | nucleic acid bases, sugars, phosphoric acid | 
 |  | The origins of the building blocks | 
 |  | Concentrating the building blocks | 
 |  | nucleic acids bases, sugar, phosphoric acid to nucleic acids (DNA, RNA) | 
 |  | Catalyzed reactions on clay minerals | 
 |  | amino acids and nucleic acid bases are attracted and bind to clay minerals | 
 |  | Combining the building blocks into a self-replicating cell | 
 |  | enclosing an environment of proteins, DNA, RNA, ATP and their building blocks. | 
 |  | Once life was established it would consume the organic building blocks. | 
 
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